Adjusting my carbs a few weeks ago, I found the throttle spindles were quite sloppy which was causing idling difficulties. I contacted Gower and Lee in the UK and purchased a bushing kit to tighten things up. The kit consisted of two bushings and a new throttle spindle (the spindles and their housings both wear). I was advised to line drill the holes in the carb where the spindle rotates and install the bushings and new spindles. My machinist did so and returned the carbs with "like new" tolerances.

The operation tamed the erratic idle, however I couldn't adjust the idle below 3000 rpm. Examining the bushings, I discovered that they had been inset from the carburettor wall by a couple of millimetres. I surmised that this created a bypass for air around the butterfly, even when it was closed completely. I returned the carbs to my machinist who said the bushings had to be inset so they would not bind on the butterfly and in any event this gap would not impact performance. I consulted Gower and Lee who advised me similarly, that this was the way they installed theirs as well.

After much head scratching and consultation with others, I could come up with no other conclusion than that the gap was causing the issue. I returned the carbs to my machinist and asked him to humour me and tighten up the gap and the problem was solved. Just an FYI.